Thermionic oscillation generator



March 24, 1936.

B. J. WlTT ET AL.

THERMIONIC OSCILLATION GENERATOR Filed Dec. 18, 1951 GRID VOLTS muumiiji zkzuixzu ueo2 INVENTOR B-J WITT BY C. FRANKLI K RNEY Patented Mar. 24, 1936 UNITED Charles Samuel Fra nklin,

Strand, London,

England, assignors to Radio Corporation of America, a corporation of Delaware Application December 1 In Great Britain 8, 1931, Serial No. 581,794 December 20, 1930 1 Claim. (01. 250-36) This invention relates to thermionic oscillation generators and more particularly to thermionic oscillation generators for generating short waves.

The invention has for its object to provide an improved thermionic oscillation generator, suitable for generating short waves, in which the frequency generated shall only vary slowly, if at all, with change in very small.

According to this invention a thermionic oscillation generator arrangement suitable for use for generating short waves comprises, in combination, a master frequency determining circuit, an amplifier tube having its input circuit coupled to said master circuit, a second amplifier tube having its input circuit coupled to the tube.

In one way of carrying out the invention an oscillation generator comprises a master frequency determining circuit which is associated with the input circuit of a first amplifier tube, the grid of said tube being capacity coupled to said master circuit, an anode resistance in the anode circult of said tube, a further tube having its input circuit capacity coupled to the anode of said first amplifier tube, said further tube having a tuned circuit in its anode circuit and a second amplifying tube having its input circuit capacity coupled to the anode of the first amplifier tube and its anode capacity coupled back to the master circuit, an anode resistance being provided in the anode circuit of said last tube.

The invention is illustrated in the accompanying drawing in which Figure 1 shows an arrangement embodying a master frequency determining circuit which may conveniently consist of a unit as described in United States Patent No. 2,028,596, granted January 21, 1936, to C. S. Franklin et al., and Figures 2 and 3 show graphically the characteristics of the amplifying tubes V1 and V2 employed in the circuit of Figure 1. The frequency determining arrangement as disclosed and illustrated in said patent and illustrated in Figure 1 of this application includes a coil L and a condenser C, each having one terminal connected to screen E and the other terminal conected with small condensers X and Y as shown, the whole arrangement being enclosed within an earthed screening case E. The variable capacity C and the inductance L form the princi- 5' pal elements of the frequency determining circuit which is enclosed in the shield E. As pointed out more in detail in said patent, the elements X, Y, C, and L are enclosed in said shield E,

among other things, to maintain the same at 10 an even temperature free of moisture, etc., so that the frequency determined thereby will be constant or nearly so. Furthermore, as pointed out in detail in said patent, the elements, and in nected to the earthed cathode F1 of said tube 30 through a resistance GR1. The anode of tube V1 is connected to the positive terminal of a source of anode potential AB through an anode resistance AR1, and is also connected through a coupling condenser is suitably positively biassed by a source of potential not shown which may be connected thereto. The plate circuit of the tube SV contains a tuned circuit mm which 40 is adapted to be coupled through condensers m n to the first amplifier stage of a radio or similar transmitter (not shown) or to frequency changing circuits as may be required. The circuit L101 may be tuned to the same frequency as 45 the master frequency determining circuit or to a harmonic thereof. The anode of tube V1 is also connected through a condenser P and an oscillation damping resistance SR (sometimes termed as anti-squegger resistance) to the 50 grid of a second amplifying tube V2 whose anode A2 is connected through an anode resistance ARz to the source of anode potential and whose grid G2 is connected through a resistance GRz to the cathode F2 of said tube, said cathode being 55 The high potential 5 O to the control grid GS of 35 what mannerthe same is to be earthed. The anode A2 is connected through a coupling condenser X to the unearthed end of the frequency determining circuit. The screen E serves as the earth point and common cathode point and the negative terminal of the source AB is connected thereto. In operation the tubes V1 and V2 serve to maintain the master frequency determining circuit in oscillation, the tube SV serving as an amplifier and coupling tube between said circuit and the amplifier or other device which is coupled through condensers 1;.

The following components and circuit Values have been found in practice to give satisfactory results as regards relative constancy of frequency with varying filament current and (within limits) varying anode potentials:-

The amplifying tube V1 is known as the L610. This is a tube of about 7500 ohms impedance having a mutual conductance of 2.0 Ma/volt and provided with a filament taking 0.1 amperes at 6 volts. At 100 volts anode potential and with no grid voltage the amplification factor is 15. The characteristics of an L610 tube are shown graphically in Figure 2 of the drawing. With this tube in circuit the value of the grid resistance G31 was 75,000 ohms and that of the anode resistance AR1, L000 ohms.

The second amplifying tube V2 is known as the P610. This is a tube of about 35.00 ohms impedance havin a mutual conductance of 2.28 Ma/volt and has a filament taking 0.1 amperes at 6 volts. The amplification factor when the anode voltage is 100 and grid voltage zero is 8. The characteristics of a P010 tube are shown graphically in Figure 3. With this tube the value of the grid resistance GRz was 30,000 ohms and the anode resistance AM, 4,000 ohms.

Having now particularly described and ascertained the nature of our said invention and in ri r ed we de la t a w a W cla m 15 A constant frequency oscillation generator circuit comprising, in combination, a master frequency determining circuit including inductance and capacity enclosed in a metallic screen, an amplifier tube having an anode, cathode, and control electrode, said cathode being directly connected to and said control electrode resistively connected to said metallic screen, said control electrode being coupled to one terminal of said master frequency determining circuit, a second amplifier tube having an anode, cathode, and control electrode, said last cathode being directly connected to and said last control electrode resistively connected to said metallic screen, a connection including a resistance and a condenser in series between the control electrode of said second tube and the anode of said first tube, and a connection between the anode of said second tube and another terminal of said master circuit, a tank circuit comprising an inductance and condenser in parallel tuned to a frequency bearing a predetermined relation to the frequency of said master circuit and individual connections including re-. sistances from a point intermediate the ends of said last inductance to the anodes of both said tubes, a source of potential having one terminal connected to said last point and its other terminal connected to said metallic screen, output leads from said tank circuit from points symmetrically located with respect to said first point on said inductance, a screen grid tube also having an anode, cathode and control electrode, the cathode of said last tube being directly connected to and the control electrode thereof resistively connected to said metallic screen, said control electrode of the screen grid tube being coupled through a con-. denser to the anode of said first tube, and the anode of said screen grid tube being coupled to said tank circuit.

- BERTRAM JOHN WITT.

CHARLES SAMUEL FRANKLIN. 

